RE: Question on pattern matching

• To: mathgroup at smc.vnet.net
• Subject: [mg47792] RE: [mg47765] Question on pattern matching
• From: "David Park" <djmp at earthlink.net>
• Date: Tue, 27 Apr 2004 04:46:36 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```Roman,

Certainly not a stupid question! You would be astonished at how much so
called "experts" learn from so called "stupid" questions.

SetAttributes[k, Orderless]

k[a, b, b] /. k_[x_, x_, y_] -> 0
k[a, b, b]

Since you used a pattern, k_, on the lhs of the rule Mathematica did not
associate it with the actual k for which you set the Attributes.

The following works.

k[a, b, b] /. k[x_, x_, y_] -> 0
0

David Park

From: Roman Green [mailto:rgreen at mail.ru]
To: mathgroup at smc.vnet.net

Hi,

I am a very newbie in Mathematica so sorry for possibly stupid question.

In the following Mathematica's output
In[1]:= SetAttributes[k, Orderless]
In[2]:= k[a, b, b] /. k[x_, x_, y_] -> 0
Out[2]= 0
In[3]:= k[a, b, b] /. k_[x_, x_, y_] -> 0
Out[3]= k[a, b, b]

I can't understand why Mathematica can find match when applying pattern
k[x_, x_, y_], but is unable with more general pattern k_[x_, x_, y_].

---

R. Green

```

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